“Flip chip” is a common process with which microelectronic devices, such as semiconductor devices, are electrically and mechanically coupled to a substrate, such as a circuit board or other type of circuit carrier. In general the “flip chip” process allows a die or chip to be directly coupled to the substrate by being placed faced down (i.e. “flipped”) on the substrate instead of the die being placed “face-up”. This older “face-up” technology is commonly called “wire bonding” and uses wires to connect to each contact pad of the substrate. “Flip chip” provides an alternative to “wire bonding” that includes advantages in its small size, performance, flexibility, reliability and cost. “Flip chip” is often used in smaller electronic devices such as cell phones, digital music players, personal data assistants and data storage systems.
There are generally three stages to assembling a “flip chip”. First, the die is bumped with a conductive material. Next, the bumped die is attached to the substrate. Lastly, the remaining spaces under the die are filled with a non-conductive material that strengthens the otherwise fragile connection provided by the bumped conductive material, protects the bumps and compensates for any thermal expansion difference between the die and the substrate. Examples of different kinds of bumping include solder bumping, plated bumping, gold stud bumping and conductive adhesive bumping.
One significant disadvantage of the “flip chip” is the delicate surface of the die that is exposed after it is “nipped” and underfilled. The exposed side of the die is vulnerable to mechanical damage, especially semiconductor dies which are susceptible to damage caused by the brittle nature of the elemental silicon that the semiconductor die is made of. Small particles of elemental silicon can emanate from mechanical damage sites that are commonly found on the edges of the exposed surface. In addition, small particles of elemental silicon can emanate from various places on the semiconductor die depending on manufacturing conditions. Regardless of how these small particles emanate from the semiconductor die, these particles can damage the electronic devices that the “flip chip” is positioned in.
In order to eliminate the particulation of mechanical damage sites on a die and particulation due to manufacturing of the die, often, a die can be totally encapsulated or coated with a backside film coating. Although an encapsulated die or backside film coated die is protected or somewhat protected from inadvertent contact damage, an encapsulated die or backside film coated die have process and cost limitations. Complete encapsulation of the die requires a secondary process, which results in a significant cost increase to the finished assembly. In addition, certain small-sized electronic devices that include design space limitations cannot tolerate the material that flows away from the die that occurs during full encapsulation. Backside film coating of the die does provide a degree of protection from near-perpendicular impacts to the backside of the “flip chip”, however, backside film coating does not protect the edges or corners of the die. Thus, backside film coating does not protect against the most common source of particulation from the die.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.